1. Field of the Invention
This invention relates generally to negative supply, low-voltage detection circuits, and more particularly, to a system and method for detecting a negative supply, low-voltage supply fault without the need for a current mirror.
2. Description of the Prior Art
Modern negative supply (VEE), low-voltage detection circuits such as the detection circuit 100 illustrated in FIG. 1, generally employ a current mirror (depicted as Q15, Q16 and Q24) that takes the current in a resistor string 102 to VEE, and then supplies this current to a plurality of detection resistors such as resistors R42-R44 illustrated in FIG. 1 as if coming from a positive supply. With continued reference to FIG. 1, the voltage generated via the detection resistors R42-R44 is then compared to a reference voltage such as that applied at the base of transistor Q5. This process requires generating a pseudo ground reference using transistors such as Q17 and Q18 along with a bipolar PNP or a PMOS transistor current mirror such as Q15, Q16 and Q24, all of which occupy area, consume power, and introduce unwanted errors. Those skilled in the art will readily appreciate that PMOS and PNP mirrors are notorious for their inaccuracies if sophisticated techniques are not employed to reduce the unwanted errors. The negative supply, low-voltage detection circuit 100 utilizes an additional 80 xcexcA of current to bias on transistor Q17; and the current from the VEE resistor string 102 sets up a nominal 100 xcexcA of current which spans the full supply from VEE to VCC (typically xe2x88x925V to +5V), and is mirrored again back to Ground.
In view of the foregoing, it would be desirable and advantageous to provide a technique capable of detecting a negative supply, low-voltage supply fault and that does not require a current mirror.
The present invention is directed to a system and method for detecting a negative supply, low-voltage supply fault without the need for a current mirror.
In one aspect of the invention, a negative supply, low-voltage detection circuit is is implemented to detect a negative supply, low-voltage supply fault without the inaccuracies generally associated with a current mirror.
In another aspect of the invention, a negative supply, low-voltage detection circuit is implemented to consume less power than known negative supply, low-voltage detection circuits that employ a current mirror.
In yet another aspect of the invention, a negative supply, low-voltage detection circuit is implemented without a current mirror and its associated support circuitry.
One embodiment of the invention is directed to a circuit for detecting a negative supply, low-voltage fault comprising a negative supply voltage, a circuit Ground, a circuit configured to generate a reference voltage, a resistor string coupling the negative supply voltage to the reference voltage and having a tap configured to provide a tap voltage that will be at a ground level voltage defined by the circuit Ground when the negative supply voltage reaches a desired threshold level, and a circuit configured to compare the tap voltage and the ground level voltage and generate an output signal when the negative supply voltage reaches the desired threshold level.
Another embodiment of the invention is directed to a circuit for detecting a negative supply, low-voltage fault comprising a negative supply voltage, a circuit Ground, means for generating a reference voltage, a resistor string coupling the negative supply voltage to the reference voltage and having a resistor tap that will be at a ground level voltage defined by the circuit Ground when the negative supply voltage reaches a desired threshold level, and means for comparing the resistor tap voltage with the ground level voltage to generate an output signal when the negative supply voltage reaches the desired threshold level.
Still another embodiment of the invention is directed to a method of detecting a negative supply fault comprising the steps of providing a negative supply, low-voltage detection circuit devoid of current mirrors and having a negative supply voltage, a circuit Ground, means for generating a reference voltage, a resistor string coupling the negative supply voltage to the reference voltage and having a resistor tap that will be at a ground level voltage defined by the circuit Ground when the negative supply voltage reaches a desired threshold level, and a comparator; comparing the resistor tap voltage with the ground level voltage; and generating an output signal when the negative supply voltage reaches the desired threshold level.